What does processing mean and why does it take so long

I just uploaded a video that was quite small in size and it took almost 1-hour to finish --it then said it was "processing" and please wait. It has been in this status for 45 minutes. Can anyone tell me why this is taking so long, is it okay to close out of it?

You can close out of it -- the video is now entirely on the server, and nothing you can do with your browser will affect it.

But before you do, just reload the page. It's possible the video has already finished processing. Your browser actually has no way of knowing what's happening on YouTube's end, and it will only get up-to-date information if you tell it to ask the server (by reloading the page).

"Processing" means this: YouTube must convert your video into several different formats which can be played in the YouTube player. First is a low quality version that will play on very old computers (and looks really horrible). Then there will be a standard quality version which looks a lot better, and there may also be either a high quality or a high definition version. There will also be a version which will play on smartphones.

Preparing all these different versions takes a little time. It shouldn't take more than a few minutes, but sometimes it might take a little longer. If it still hasn't finished processing after about 8 hours, you can assume that something has gone wrong.

If the upload is complete and it's processing, you can turn your computer off if you want. It's done. Processing is the re-encoding of the video into the number of various formats YouTube uses, and it can take from a few minutes to a few hours, depending on the format you uploaded, the size, how busy YouTube's servers are, and a number of other variables.